Dams are a useful source of energy. An embodiment of a dam according to the present invention includes precast segments configured to be coupled together to form a dam optionally used to generate energy. An embodiment includes a spillway extender to prevent upstream or downstream erosion of a riverbed at the dam. An underpinning system may be employed to assist in maintaining position of the dam or segmental components. Solar panel energy generation systems and battery storage may be associated with the segmental dam to store energy and, optionally, produce auxiliary power for subsystems associated with the dam, such as for supporting automated spillway control gate level control or automated gearing system control to control a gear ratio associated with rotating or other moving parts used to convert kinetic energy of water into electrical energy.